Typically, programmable controllers have been constructed with input/output systems being interconnected with the programmable controller in a manner which would require the external devices being controlled thereby to be disconnected whenever a particular input/output panel is removed, replaced, or rearranged. Consequently, costly, time consuming effort is generally required in these prior art systems to disconnect the input/output terminals from the various external equipment and, afterwards, effectuate the reconnection of the equipment in the desired manner.
In addition, the prior art system must be shut down in order to make the desired or required changes to an individual input/output circuit. Since shutdowns result in expensive down time, additional costs are incurred in replacing and removing input/output circuits from these prior art systems.
More recently, advances have been made in modular input/output panel constructions for programmable controllers. These more recent prior art systems have resolved some of these prior art difficulties by achieving an input/output assembly which does not require complete shutdown of the programmable controller and allows the external equipment wiring to remain in their original connections while the input/output module is removed, replaced or repaired. These systems represent the best prior art patents of which we are aware and are exemplified in U.S. Pat. No. 3,942,077 of Howard A. Powers.
In Powers, input/output modules are taught which are capable of being directly plugged into an input/output panel housing which incorporate fixed terminals to which the external equipment is connected. In this way, the previous necessity for disconnecting the external equipment wiring during removal or replacement of the input/output modules is eliminated.
In addition to Powers, Jay M. Prager and Joseph F. Sadlow have a patent application pending in the U.S. Patent and Trademark Office relating to a Modular Panel Construction for Programmable Controller bearing Ser. No. 883,277 and filed Mar. 3, 1978 now U.S. Pat. No. 4,215,386. This patent application, the references cited therein, and Powers represents the best prior art of which I am aware.
Although the Prager and Sadlow patent application discloses a system which overcomes some of the drawbacks experienced with the input/output module system of Powers, both Powers and Prager and Sadlow require the use of modules, wherein each module serves as an independent housing for a particular printed circuit board. Prager and Sadlow have achieved a system which has made substantial advances over the input/output module disclosed in Powers, however, the input/output module disclosed in their patent application has been unable to meet the demands and constraints imposed upon systems wherein only the printed circuit board is mounted, without a separate modularized housing supportingly containing the printed circuit board.
In particular, these prior art plug-in input/output modules are not able to meet the different requirements for being both panel mounted or rack mounted, without required specially design adaptors. Also, the prior art modules have been found to require a greater area per input/output than various users have available as well as being generally unable to meet all of the various standards and requirements imposed upon a single system throughout the world.
Therefore, it is the principal object of this invention to provide an input/output system, for interconnection with a central processor to form a programmable machine controller, which supportingly maintains a plurality of input/output printed circuit boards in readily accessible positions for quick and easy insertion, removal and replacement of the printed circuit board without necessitating removal of the external devices electronically engaged thereto.
Another object of this invention is to provide an input/output system having the characteristic features defined above wherein the printed circuit board can be simply positioned in a holder and rapidly and easily moved into secure and complete electronic engagement with both the external devices and the central processor.
Another object of this invention is to provide an input/output system having the characteristic features defined above which is capable of rapid assembly and disassembly without requiring soldering, thereby assuring easy and reliable field maintenance while also being reliable and reasonably priced.
A further object of the present invention is to provide an input/output system having the characteristic features defined above which is quickly and easily expanded by simply assembling and interconnecting additional units up to the maximum capabilities of the central processor.
Another object of this invention is to provide an input/output system having the characteristic features defined above which is capable of meeting all world-wide standards as well as being capable of being either rack mounted or panel mounted.
Another object of this invention is to provide an input/output system having the characteristic features defined above as well as having a high input/output density, thereby providing a maximum number of input/output points per square area as is feasible.
Other and more specific objects will in part be obvious and will in part appear hereinafter.